This invention relates to metal/ceramic composites and more particularly to silver metal-coated superconducting ceramic powders.
Since the advent of the new generation high Tc (.about.77.degree. K.) ceramic superconducting materials, prodigious efforts have been expended to fabricate the same into usable wire form.
The relative metallurgical intractability of these ceramic compounds has been described as follows:
". . . They are reactive, unstable, brittle, unable to support any significant stress, unable to be formed and reprocessed, and not easily joined. The powder form of the compound used as the raw material for the fabrication process is itself not easily produced with consistency." PA0 "There is a great deal of uncertainty about compositions and structures which superconduct (and remain superconducting after processing), but clearly, in the new materials, oxygen stoichiometry and oxygen partial pressure during processing are crucial. Attempts to combine these powders with metal-matrix support systems such as copper have been unsuccessful because elevated-temperature fabrication in the rich oxygen environment these powders require causes rapid oxidation of the metals and rapid degradation of the powder, including oxygen depletion of the superconducting lattice." PA0 [Murr, L.E. Hare, A.W., Eror, N. G. "introducting: The metal-Matrix High-Temperature Superconductor, " Advanced Materials & Processes, Inc., Metal Progress October 1987. PA0 (1) mixing AgNO.sub.3 with superconducting ceramic powder particles; PA0 (2) melting the AgNO.sub.3 so that it wets and forms a uniform coating over the surfaces of the particles; and PA0 (3) decomposing the AgNO.sub.3 to form a thin, uniform coating of silver metal on the surfaces of the particles.
It would be desirable to provide a process by which intimate bonding of the superconductive ceramic particles with a suitable workable metal of good electrical conductivity is achieved while maintaining the superconductive properties of the ceramic.